Here is the page from the PET showing many of the parts in question including the expansion valve (4) and the 'electric motor central (control?) valve' (6) that may help you out.
HVAC detail .pdf
I know this is not the problem you have but my A/C had a problem where the expansion valve was stuck open. The A/C was ice cold when first turned on but after 10 minutes or so the system would freeze up solid and no air would flow through the vents. The expansion valve was replaced, the system recharged and it has worked to spec ever since.
Is it possible your expansion valve is not opening at all? They can get plugged.
Threaded Mode
